Radio transmission device and transmission rate decision method

ABSTRACT

A base station apparatus (radio transmission apparatus) transmits a radio signal of data to a mobile terminal apparatus (communication apparatus of a transmission destination). The mobile terminal apparatus receiving the radio signal determines (ST 1010 ) information (CQI) on a downlink transmission rate enabling reception in the mobile terminal apparatus based on reception quality such as CIR to transmit to the base station apparatus. The base station apparatus extracts a CQI value from the received radio signal, while obtaining likelihood of received data (ST 1020 ), and corrects the CQI value based on the likelihood (ST 1030 ). Then, based on the corrected CQI value, the base station apparatus determines a downlink transmission rate (ST 1040 ). By this means, even when the radio transmission apparatus erroneously receives the transmission rate request transmitted from the communication apparatus of the transmission destination, the communication apparatus is prevented from erroneously receiving the data transmitted from the radio transmission apparatus.

TECHNICAL FIELD

The present invention relates to a radio transmission apparatus used ina wireless communication system for performing high-speed packettransmission, and to a method of determining a downlink transmissionrate used in the apparatus.

BACKGROUND ART

Developed in the field of wireless communications are systems where aradio transmission apparatus transmits packets at high speed to acommunication apparatus that is a transmission destination of thepackets, and particularly, downlink high-speed packet transmissionsystems where a plurality of mobile terminal apparatuses shares ahigh-speed large-capacity downlink channel, and a base station apparatustransmits packets to the mobile terminal apparatuses. Among the downlinkhigh-speed packet transmission, as a higher packet transmission systemof IMT-2000, the system called HSDPA (High Speed Downlink Packet Access)is considered for the purpose of increasing the downlink peaktransmission speed, decreasing transmission delay, and achieving highthroughput and the like. As techniques constituting HSDPA, disclosed in3GPP (3rd Generation Partnership Project) is the transmission systemcalled AMC (Adaptive Modulation and Coding) (see 3GPP TR25.848 “Physicallayer aspects of UTRA High Speed Downlink Packet Access).

The AMC technique is to vary adaptive modulation parameters such as theM-ary number, error correcting coding rate and the like adaptively athigh speed corresponding to variations in channel quality. In the AMCtechnique, as the channel quality is higher, the transmission rate canbe increased by using a large M-ary number and high coding rate. Morespecifically, each mobile terminal apparatus measures downlinkpropagation path environments whenever necessary, and transmits anadaptive modulation request (CQI: Channel Quality Indicator) based onthe measurement result to a base station apparatus. The CQI correspondsto a pair of adaptive modulation parameters. Based on the CQI, the basestation apparatus determines a mobile terminal apparatus that is atransmission destination of transmission data, concurrently determinesan optimal transmission rate, and transmits the transmission data.

Considered as the adaptive modulation parameters are the M-ary number(for example, switching between QPSK (Quaternary Phase Shift Keying) and16QAM (Quadrature Amplitude Modulation)), coding rate (for example,performing turbo coding at R=⅓ and varying by puncturing or repetition)and the like. Meanwhile, used as the channel quality information is, forexample, CIR (Carrier to Interference Ratio), SIR (Signal toInterference Ratio), transmit power of a dedicated channel (for example,DPCH (Dedicated Physical Channel)), and the like.

However, in the conventional system, when the base station apparatuserroneously receives the CQI transmitted from a mobile terminalapparatus, and transmits downlink data to the mobile terminal apparatusat a transmission rate determined based on the erroneously received CQI,the mobile terminal apparatus also erroneously receives the data becausethe data is transmitted at a transmission rate different from therequested one, and as a result, repeats retransmission of data, andthere arises a problem of decreasing the throughput. In particular,although the mobile terminal apparatus transmits a request for a lowtransmission rate i.e. request for a low value of CQI (low CQI), whenthe base station apparatus erroneously receives the request as a hightransmission rate i.e. request for a high value of CQI (high CQI), andtransmits data to the mobile terminal apparatus at a high transmissionrate based on the erroneous CQI, the mobile terminal apparatus does notmeet the quality required of the transmitted high transmission rate, andthere is a high possibility of erroneously receiving the data.

DISCLOSURE OF INVENTION

In a communication system where a radio transmission apparatusdetermines a transmission rate of transmission data based on atransmission rate request transmitted from a communication apparatusthat is a transmission destination of a packet, when the radiotransmission apparatus erroneously receives a transmission rate request,since the transmission apparatus transmits downlink data at atransmission rate determined based on the erroneously receivedtransmission rate request, a possibility is high for the communicationapparatus to erroneously receive the data. Accordingly, the reliabilityof a transmission rate request received in the radio transmissionapparatus is an important factor to maintain good communicationenvironments in the communication system.

The inventor noticed this respect, found out that it is possible tomaintain good communication environments by evaluating the reliabilityof a transmission rate request received in the radio transmissionapparatus using likelihood of data received in the radio transmissionapparatus, and correcting the transmission rate request to a lowerrequest when the reliability of the transmission rate request is low,and reached the present invention. Herein, the likelihood of thereceived data includes a soft-decision value, reception SIR, receptionlevel and the like.

In other words, it is an object of the present invention to prevent acommunication apparatus from erroneously receiving data transmitted froma radio transmission apparatus even when the radio transmissionapparatus erroneously receives a transmission rate request (CQI)transmitted from the communication apparatus that is a transmissiondestination of a packet, and to maintain the throughput of the entirecommunication system.

The object is achieved by the radio transmission apparatus correctingthe received transmission rate request based on the likelihood ofreceived data, and determining a downlink transmission rate based on thecorrected transmission rate request.

In descriptions hereinafter, it is assumed that the radio transmissionapparatus is a base station apparatus, and that the communicationapparatus of the transmission destination is a mobile terminalapparatus. More specifically, as shown in FIG. 1, the base stationapparatus transmits a radio signal of data to the mobile terminalapparatus. The mobile terminal apparatus receiving the radio signaldetermines (ST1010) information (CQI) on a downlink transmission rateenabling reception in the terminal apparatus based on reception qualitysuch as CIR to transmit to the base station apparatus. The base stationapparatus extracts a CQI value from the received radio signal, whileobtaining likelihood of received data (ST1020), and corrects the CQIvalue based on the likelihood (ST1030). Then, based on the corrected CQIvalue, the base station apparatus determines a downlink transmissionrate (ST1040). Thus, since the base station apparatus transmits downlinkdata at a low transmission rate determined from the corrected CQI, anerror rate of received data is decreased in the mobile terminalapparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram to explain a general outline of the invention;

FIG. 2 is a block diagram illustrating a configuration of a base stationapparatus according to Embodiment 1 of the invention;

FIG. 3 is a block diagram illustrating a configuration of a mobileterminal apparatus according to Embodiment 1 of the invention;

FIG. 4 is a block diagram illustrating an internal configuration of aCQI value correcting section according to Embodiment 1 of the invention;

FIG. 5 is a flow diagram illustrating procedures of a method ofdetermining a transmission rate according to Embodiment 1 of theinvention;

FIG. 6 is a graph to explain a method of correcting a CQI valueaccording to Embodiment 1 of the invention;

FIG. 7 is another graph to explain the method of correcting a CQI valueaccording to Embodiment 1 of the invention;

FIG. 8 is a block diagram illustrating a configuration of a CQI valuecorrecting section according to Embodiment 2 of the invention;

FIG. 9 is a flow diagram illustrating procedures of a method ofdetermining a transmission rate according to Embodiment 2 of theinvention;

FIG. 10 is a graph to explain a method of correcting a CQI valueaccording to Embodiment 2 of the invention;

FIG. 11 is a flow diagram of summarized procedures of the method ofdetermining a transmission rate according to Embodiment 2 of theinvention;

FIG. 12 is another graph to explain the method of correcting a CQI valueaccording to Embodiment 2 of the invention;

FIG. 13 is a block diagram illustrating a configuration of a basestation apparatus according to Embodiment 3 of the invention;

FIG. 14 is a diagram illustrating a frame structure of HS-DPCCH;

FIG. 15 is a block diagram illustrating another configuration of thebase station apparatus according to Embodiment 3 of the invention; and

FIG. 16 is a block diagram illustrating a configuration of a basestation apparatus according to Embodiment 4 of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will specifically be describedbelow with reference to accompanying drawings.

Embodiment 1

FIG. 2 is a block diagram illustrating a configuration of base stationapparatus 100 according to Embodiment 1 of the invention, and FIG. 3 isa block diagram illustrating a configuration of mobile terminalapparatus 150. Herein, a case is explained as an example where a softdecision value is used as likelihood of received data. In addition, thesoft decision value represents amplitude information, phase information,amplitude information and phase information, Euclidean distance from areference signal point and like after despreading.

In FIG. 2, base station apparatus 100 has transmission frame generatingsection 101, modulation section 102, spreading section 103, radiotransmission section 104, antenna duplexer 105, antenna 106, radioreception section 111, despreading section 112, demodulation section113, decoding section 114, CQI value correcting section 115 andtransmission rate determining section 116.

In FIG. 3, mobile terminal apparatus 150 has antenna 151, antennaduplexer 152, radio reception section 153, despreading section 154,demodulation section 155, decoding section 156, CIR measuring section157, CQI determining section 158, transmission frame generating section161, modulation section 162, spreading section 163 and radiotransmission section 164.

In base station apparatus 100, transmission frame generating section 101generates a transmission frame from transmission data to output tomodulation section 102. Modulation section 102 modulates a signal outputfrom transmission frame generating section 101 to output to spreadingsection 103. Spreading section 103 performs spreading on the modulatedsignal to output to radio transmission section 104. Radio transmissionsection 104 performs predetermined radio processing on the spreadsignal, and transmits the signal to mobile terminal apparatus 150 viaantenna duplexer 105 and antenna 106.

In mobile terminal apparatus 150, radio reception section 153 receivesthe radio signal transmitted from base station apparatus 100 via antenna151 and antenna duplexer 152, and performs predetermined radioprocessing on the signal to output to despreading section 154.Despreading section 154 performs despreading on the signal output fromradio reception section 153 to output to demodulation section 155 andCIR measuring section 157. Demodulation section 155 demodulates thesignal output from despreading section 154 to output to decoding section156. Decoding section 156 decodes the demodulated signal and obtainsreceived data. CIR measuring section 157 measures CIR of the signaloutput from despreading section 154 to output to CQI determining section158. Based on the measured CIR, CQI determining section 158 determinesdownlink transmission rate information (CQI) enabling reception in theapparatus 150 to output to transmission frame generating section 161. Inaddition, CQI may be determined from other information except CIR. Forexample, SIR may be measured to determine CQI from the measured SIR.

Meanwhile, transmission frame generating section 161 generates atransmission frame from transmission data to output to modulationsection 162. At this point, the CQI output from CQI determining section158 is embedded in the transmission frame as well as the transmissiondata. Modulation section 162 modulates the transmission frame outputfrom transmission frame generating section 161 to output to spreadingsection 163. Spreading section 163 performs spreading on the modulatedsignal to output to radio transmission section 164. Radio transmissionsection 164 performs predetermined radio processing on the spreadsignal, and transmits the signal to base station apparatus 100 viaantenna duplexer 152 and antenna 151.

In base station apparatus 100, radio reception section 111 receives theradio signal transmitted from mobile terminal apparatus 150 via antenna106 and antenna duplexer 105, and performs predetermined radioprocessing on the signal to output to despreading section 112.Despreading section 112 performs despreading on the signal output fromradio reception section 111 to output to demodulation section 113.Demodulation section 113 demodulates the signal output from despreadingsection 112 to output to decoding section 114. Decoding section 114decodes the demodulated signal output from demodulation section 113 andobtains received data. At this point, a soft decision value obtained indecoding is output to CQI value correcting section 115. Further, a CQIvalue is extracted from the decoded signal, and also output to CQI valuecorrecting section 115.

Based on the soft decision value output from decoding section 114, CQIvalue correcting section 115 corrects the CQI value also output fromdecoding section 114, and outputs the corrected CQI value totransmission rate determining section 116. Based on the corrected CQIvalue, transmission rate determining section 116 determines atransmission rate of the transmission data to output to transmissionframe generating section 101. Based on the transmission rate notifiedfrom transmission rate determining section 116, transmission framegenerating section 101 generates a transmission frame.

One example of procedures of a method of determining a transmission ratein base station apparatus 100 will be described below with reference toFIGS. 4 and 5.

FIG. 4 is a block diagram illustrating an internal configuration of CQIvalue correcting section 115. FIG. 5 is a flow diagram illustratingprocedures of the method of determining a transmission rate in basestation apparatus 100.

The CQI received (ST1310) via antenna 106, antenna duplexer 105 andradio reception section 111 is given predetermined processing indespreading section 112, demodulation section 113 and decoding section114 and output to CQI value correcting section 115. CQI value correctingsection 115 has comparing section 121 and CQI replacing section 122.Comparing section 121 compares the soft decision value output fromdecoding section 114 with a predetermined threshold (ST1320). When thesoft decision value is less than or equal to the threshold, the CQI isregarded as being erroneously received, and CQI replacing section 122corrects the CQI value output from decoding section 114 (ST1330) tooutput to transmission rate determining section 116. When the softdecision is more than the threshold in ST1320, CQI replacing section 122outputs the CQI value itself output from decoding section 114 totransmission rate determining section 116. Based on the CQI value outputfrom CQI value correcting section 115, transmission rate determiningsection 116 determines a transmission rate of transmission data(ST1340).

The correction of CQI value is made as shown in FIG. 6. As an example, acase is described herein that CQI takes four values, CQI#1 to #4. Whenthe soft decision value output from decoding section 114 is softdecision value 1 as shown by P1, P2, P3 and P4, since the soft decisionvalue is larger than the threshold, correction is not made to the CQIvalue. Meanwhile, when the soft decision value is soft decision value 2as shown by P5, P6, P7 and P8, since the soft decision value is smallerthan the threshold, correction is made to the CQI value. By thecorrection to the CQI value, the current CQI value is replaced with aCQI value lower than the current CQI value by some steps. For example,in the setting to replace a CQI value with a one-step lower CQI value,by the correction to the CQI value, CQI#3 for P7 is replaced with CQI#2,and CQI#2 for P6 is replaced with CQI#1.

In addition, although the case is described herein as an example where acorrection width of the CQI value is constant irrespective of a level ofthe soft decision value, the correction width may be made variablecorresponding to the soft decision value. For example, as shown in FIG.7, it may be possible that when a soft decision value is soft decisionvalue 2, since the soft decision value is smaller than threshold 2 andlarger than threshold 1, the CQI value is replaced with a value smallerby one step, and that when a soft decision value is soft decision value3, since the soft decision value is smaller than threshold 1, the CQIvalue is replaced with a value smaller by two steps. It is therebypossible to correct the CQI value to a further lower value when the softdecision value is low.

Thus, according to this Embodiment, the base station apparatus regardsthe CQI as being erroneously received when a soft decision value islower than a threshold, replaces the decoded CQI value with a CQI valuelower than the decoded value, and transmits downlink data at a lowtransmission rate determined from the lower CQI, whereby the mobileterminal apparatus is capable of meeting the predetermined qualityrequired of the low transmission rate, and receiving the data withouterror. Further, by this means, it is considered decreasing the number oftimes the mobile terminal apparatus requests retransmission of data,whereby decreases in throughput can be prevented which are caused by theoriginally low CQI being erroneously received as a high CQI.Furthermore, since the main operation is making a determination usingthresholds, it is possible to implement the CQI correction operation ina simplified configuration. Moreover, the correction method can bevaried optionally by only changing the threshold, and therefore, theadjustment of the correction method is also easy.

Particularly, the soft decision value is directly used as likelihood ofHS-DPCCH (Dedicated Physical Control Channel (uplink) for HS-DSCH) usedin transmitting the CQI, and therefore, reflects the reliability of thereceived CQI accurately.

Further, when the soft decision value is less than or equal to thethreshold, it may be possible regarding the CQI as being erroneouslyreceived, and assigning a low priority or not assigning a priority to amobile terminal apparatus transmitting the CQI in scheduling of packettransmission.

In this way, when the reliability of received CQI is poor,communications are reduced or halted, and it is thus possible to preventdecreases in throughput of the entire communication system.

Embodiment 2

A base station apparatus according to Embodiment 2 of the invention hasthe same configuration as that of base station apparatus 100 as shown inFIG. 2 except CQI value correcting section 115 a, and only aconfiguration of the section 115 a different from that in Embodiment 1is shown in FIG. 8. In addition, the same structural elements as in CQIvalue correcting section 115 as shown in FIG. 4 are assigned the samereference numerals, and descriptions thereof are omitted.

It is a feature of this Embodiment determining a threshold used inmaking a determination on likelihood of received data with the thresholdbased on a CQI value. In other words, a level of originally received CQIvalue is considered in correcting the CQI value based on the likelihoodof received data. When the base station apparatus receives a high CQIfrom the mobile terminal apparatus, a downlink transmission rate is sethigh due to the high CQI. Accordingly, when the base station apparatuserroneously receives a low CQI as a high CQI although the mobileterminal apparatus transmits the low CQI, larger effects are imposed onthe throughput of the entire communication system. Therefore, in thisEmbodiment, in correcting a CQI value based on likelihood of receiveddata, when an originally received CQI value is high, the CQI iscorrected lower in consideration of effects on the throughput of thecommunication system to maintain good communication environments.

In FIG. 8, threshold setting section 201 has a table storing thecorrespondence relationship between the CQI value and threshold, andselects a threshold corresponding to the CQI value output from decodingsection 114 to output to comparing section 121. The other operation isthe same as in Embodiment 1. FIG. 9 is a flow diagram illustratingprocedures of the transmission rate determining method. As shown in thefigure, this method is different in step ST2010 from the transmissionrate determining method as shown in FIG. 5.

Referring to FIG. 10, described below is correction of CQI valueperformed in transmission rate determination in the base stationapparatus with the aforementioned configuration. As an example, a caseis described herein that CQI takes four values, CQI#1 to #4.

A plurality of thresholds is set in the table stored in thresholdsetting section 201 corresponding to CQI values output from decodingsection 114. More specifically, thresholds 1, 2, 3 and 4 are setrespectively corresponding to CQI #1, #2, #3 and #4. In other words,when the CQI value is a high CQI, the threshold is set higher, whilewhen the CQI value is a low CQI, the threshold is set lower. Then,comparing section 121 compares the soft decision value output fromdecoding section 114 with the threshold. When the soft decision value islower than the threshold, it is assumed that the CQI is erroneouslyreceived, the CQI value output from decoding section 114 is replacedwith a low CQI value, and the replaced value is output to transmissionrate determining section 116. When the soft decision value is largerthan the threshold, the CQI value output from decoding section 114 isoutput to transmission rate determining section 116 without beingreplaced.

For example, when the CQI value output from decoding section 114 isCQI#3 (P21 and P22), threshold 3 is applied as a threshold. When thesoft decision value output from decoding section 114 is soft decisionvalue 1 (P21), since the soft decision value is larger than threshold 3,the correction is not made to the CQI value. Meanwhile, when the softdecision value is soft decision value 2 (P22), since the soft decisionvalue is smaller than threshold 3, the correction is made to the CQIvalue. When the CQI value output from decoding section 114 is CQI#4 (P23and P24), threshold 4 is applied as a threshold, and the correction ismade to the CQI value in either case that the soft decision value outputfrom decoding section 114 is soft decision value 1 or soft decisionvalue 2, since these are smaller than threshold 4. In addition, thecorrection is made in the same method as in Embodiment 1.

Thus, according to this Embodiment, since the threshold is set higher asthe decoded CQI value is higher, even when the base station apparatuserroneously receives the CQI transmitted from the mobile terminalapparatus as a high CQI, it is possible to control a downlinktransmission rate within a suitable range, and to prevent decreases inthroughput of the entire communication system. Further, according tothis method, the operation is made possible of correcting the CQI whileconcurrently considering two parameters, likelihood of received data andthe CQI. Furthermore, since the main operation is making a determinationusing thresholds, it is possible to implement the above-mentionedoperation in a simplified configuration. Moreover, the correction methodcan be varied optionally by only changing the threshold, and therefore,the adjustment of the correction method is also easy.

In addition, although the case is explained as an example that acorrection width of CQI value (degree of correction) is constant, thecorrection width may be made variable corresponding to a level of thesoft decision value. For example, when the soft decision value is n, theCQI value is corrected to a CQI value corresponding to the maximumthreshold among thresholds smaller than n. For example, in FIG. 10, whenthe CQI value is CQI#4 and the soft decision value is soft decisionvalue 1 (P23), the CQI value is corrected to CQI#3 corresponding tothreshold 3 that is the maximum threshold among thresholds smaller thansoft decision value 1. Meanwhile, when the CQI value is CQI#4 and thesoft decision value is soft decision value 2 (P24), the CQI value iscorrected to CQI#2 corresponding to threshold 2 that is the maximumthreshold among thresholds smaller than soft decision value 2. Thecorrection width of the CQI value is thus varied corresponding to thelevel of the soft decision value. FIG. 11 shows a flow diagram ofsummarized procedures of this transmission rate determining method. Inaddition, the same steps as in the transmission rate determining methodas shown in FIG. 9 are assigned marks with the same numbers andalphabets.

Further, although the case is described herein as an example that oneCQI value is set for one threshold, as shown in FIG. 12, one CQI may beset for a plurality of thresholds. In FIG. 12, CQI takes seven values,CQI#1 to CQI#7, and one CQI is set for three thresholds. For example,thresholds 13, 14 and 15 are set corresponding to CQI#5. Then, differentCQI correction schemes are determined for each threshold such that theCQI value is corrected and decreased by two steps when the soft decisionvalue is less than or equal to threshold 15 (more than threshold 14),the CQI value is corrected and decreased by three steps when the softdecision value is less than or equal to threshold 14, and that the CQIvalue is corrected and decreased by four steps when the soft decisionvalue is less than or equal to threshold 13. It is thereby possible toadjust the correction of CQI value finely. For example, when the CQIvalue is CQI#5 and the soft decision value is soft decision value 1,since the soft decision value is less than threshold 15, the CQI valueis decreased by two steps and corrected to CQI#3.

Furthermore, when a value of the received CQI is small, since the effecton the communication system is small, any corrections may not be made tothe CQI. The processing for determining a transmission rate can therebybe simplified.

Embodiment 3

FIG. 13 is a block diagram illustrating a configuration of base stationapparatus 300 according to Embodiment 3 of the invention. In addition,the base station apparatus has a basic configuration similar to that ofbase station apparatus 100 as shown FIG. 2, and the same structuralelements are assigned the same reference numerals to omit descriptionsthereof.

It is a feature of this Embodiment using SIR (Signal-to-InterferenceRatio) of a signal received in the base station apparatus.

In FIG. 13, SIR measuring section 301 measures reception SIR fromdespread data output from despreading section 112 to output to CQI valuecorrecting section 302. Corresponding to the CQI value output fromdecoding section 114, CQI value correcting section 302 sets a thresholdhigher when the CQI value is a high CQI, while setting a threshold lowerwhen the CQI value is a low CQI. Then, the section 302 compares thethreshold with the reception SIR output from SIR measuring section 301.When the reception SIR is less than or equal to the threshold, thesection 302 regards the CQI as being erroneously received, and replacesthe CQI value output from decoding section 114 with a lower CQI value tooutput to transmission rate determining section 116. Further, when thereception SIR is more than the threshold, the section 302 outputs theCQI value output from decoding section 114 to transmission ratedetermining section 116 without replacing.

FIG. 14 illustrates a fame structure of HS-DPCCH. HS-DPCCH used intransmitting the CQI is code-multiplexed with DPCCH and transmitted fromthe mobile terminal apparatus. SIR measuring section 301 measures theSIR using the strength of a pilot signal of DPCCH. Accordingly, SIRmeasuring section 301 does not obtain the SIR of CQI (HS-DPCCH).However, HS-DPCCH and DPCCH are transmitted at the same time incode-multiplexing, and the power of HS-DPCCH is subjected totransmission control with an offset of a fixed value with respect toDPCCH, whereby the SIR can be assumed to represent likelihood of theCQI.

Thus, according to this Embodiment, the base station apparatus regardsthe CQI as being erroneously received when the reception SIR is lowerthan or equal to a threshold, replaces the CQI value with a value lowerthan the decoded CQI value, and transmits downlink data at atransmission rate lower than that determined from the CQI, whereby themobile terminal is capable of meeting the predetermined quality requiredof the low transmission rate, and receiving data without error. Further,at this time, the mobile terminal does not request retransmission, andtherefore, decreases in throughput can be prevented which are caused bythe low CQI being erroneously received as a high CQI.

Moreover, the SIR can be assumed as likelihood of HS-DPCCH for use intransmitting the CQI, and the likelihood is obtained using a pilot ofknown bits on DPCCH. It is thus possible to obtain the likelihood withmore accuracy than that of the soft decision value, and judge erroneousreception of CQI with reliability.

In addition, although the case is described herein as an example ofusing SIR as likelihood of received data, not limiting to SIR, otherreception quality may be used such as CIR (Carrier to InterferenceRatio) and RSSI (Received Signal Strength Indicator). Further, as shownin FIG. 15, a power level (reception level) of a received signal may beused as likelihood of received data. Reception level measuring section311 in base station apparatus 300 a measures a reception level fromdespread data output from despreading section 112 to output to CQI valuecorrecting section 302 a. The other operation is the same as thatdescribed previously.

Further, Embodiments 1, 2 and 3 may be combined. In other words, thesoft decision value, reception SIR and reception level may be combinedas the likelihood to correct a CQI value.

Embodiment 4

FIG. 16 is a block diagram illustrating a configuration of base stationapparatus 400 according to Embodiment 4 of the invention. In addition,the base station apparatus has a basic configuration similar to that ofbase station apparatus 100 as shown FIG. 2, and the same structuralelements are assigned the same reference numerals to omit descriptionsthereof.

It is a feature of this Embodiment detecting the moving speed of amobile terminal apparatus and corresponding to the result, providing athreshold with an offset.

In FIG. 16, moving speed detecting section 401 divides a known symbol(pilot symbol) from despread data output from despreading section 112,obtains how much a phase of a current known symbol is rotated withrespect to a phase of the last known symbol, and from this rotation,detects the moving speed of the mobile terminal apparatus to output toCQI value correcting section 402. When the moving speed is high, it ispredicted that reception performance is poorer than that in low movingspeed even in the same soft decision value. Therefore, CQI valuecorrecting section 402 sets the threshold higher than in low movingspeed. The other operation is the same as that as described previously.

Thus, according to this Embodiment, the correction of CQI is made inconsideration of also the moving speed such as adding an offset to thethreshold corresponding to the moving speed of the mobile terminalapparatus, and it is thus possible to judge erroneous reception of CQIwith more reliability and reduce an error rate of received data in themobile terminal apparatus.

In addition, this Embodiment may be combined with Embodiments 1, 2 and3. In other words, the threshold may be provided with an offsetcorresponding to the moving speed when the reception SIR or receptionlevel is used as likelihood of received data.

The transmission rate determining method according to the invention isnot limited to the base station apparatus, and applicable to radiocommunication apparatuses that determine a transmission rate oftransmission data using CQI (or information of the similar concept), andit is thus possible to provide the radio communication apparatuses withthe same advantages as described above.

Further, from the viewpoint of simplifying the apparatus, the case ismainly described herein that the correction of CQI is made using adetermination with thresholds, but the same operation may be performedusing another method. For example, a correction method (rule) may bedetermined with arithmetic equation, or stored beforehand in a datatable.

As described above, according to the invention, even when a base stationapparatus erroneously receives CQI transmitted from a mobile terminalapparatus, the mobile terminal apparatus can be prevented fromerroneously receiving data transmitted from the base station, and it ispossible to maintain the throughput of the entire communication system.

This application is based on the Japanese Patent ApplicationNo.2003-031539 filed on Feb. 7, 2003, entire content of which isexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a radio transmission apparatusused in a wireless communication system for performing high-speed packettransmission, and to a method of determining a downlink transmissionrate used in the apparatus.

1. A radio transmission apparatus that determines a transmission rate intransmitting data, based on a CQI (Channel Quality Indicator)transmitted from a communication apparatus that is a transmissiondestination of the data, comprising: a receiver that receives a signalincluding the CQI transmitted from the communication apparatus; acorrector that corrects the CQI included in the signal, based onlikelihood of the signal including the CQI; and a transmission ratedeterminer that determines a transmission rate in transmitting data tothe communication apparatus, based on the corrected CQI.
 2. The radiotransmission apparatus according to claim 1, wherein based on thelikelihood, the corrector determines a degree of correction of the CQI.3. The radio transmission apparatus according to claim 1, wherein thecorrector corrects the CQI based on a value of the CQI in addition tothe likelihood.
 4. The radio transmission apparatus according to claim3, wherein the corrector decreases the CQI more than or equal to apredetermined value to correct.
 5. The radio transmission apparatusaccording to claim 1, wherein the corrector corrects the CQI based onmoving speed of the communication apparatus in addition to thelikelihood.
 6. The radio transmission apparatus according to claim 1,wherein when the likelihood is less than or equal to a threshold, thecorrector decreases CQI to correct.
 7. The radio transmission apparatusaccording to claim 6, wherein as a value of the CQI is higher, thethreshold is set higher.
 8. The radio transmission apparatus accordingto claim 6, wherein a value of the CQI is set for a plurality ofthresholds.
 9. The radio transmission apparatus according to claim 6,wherein as moving speed of the communication apparatus is higher, thethreshold is set higher.
 10. The radio transmission apparatus accordingto claim 1, wherein the radio transmission apparatus performs schedulingin transmitting packets to a plurality of communication apparatuses, anddecreases a transmission assignment priority or does not assigntransmission to the communication apparatus subject to correction of theCQI.
 11. The radio transmission apparatus according to claim 1, whereinused as the likelihood is a soft decision value, reception quality, or areception power level of the signal including the CQI transmitted fromthe communication apparatus.
 12. A base station apparatus comprising theradio transmission apparatus according to claim
 1. 13. A mobile terminalapparatus comprising the radio transmission apparatus according toclaim
 1. 14. A transmission rate determining method for determining atransmission rate in transmitting a radio signal of data based on a CQItransmitted from a radio communication apparatus that is a transmissiondestination of the data, comprising: a reception step of receiving asignal including the CQI transmitted from the radio communicationapparatus; a correcting step of correcting the CQI included in thesignal based on likelihood of the signal including the CQI; and atransmission rate determining step of determining a transmission rate intransmitting a radio signal of data to the radio communicationapparatus, based on the corrected CQI.
 15. A transmission ratedetermining program for determining a transmission rate in transmittinga radio signal of data based on a CQI transmitted from a radiocommunication apparatus that is a transmission destination of the data,the program making a computer execute: a reception step of receiving asignal including the CQI transmitted from the radio communicationapparatus; a correcting step of correcting the CQI included in thesignal based on likelihood of the signal including the CQI; and atransmission rate determining step of determining a transmission rate intransmitting a radio signal of data to the radio communicationapparatus, based on the corrected CQI.